What is this?
PIR (passive infrared) sensor lights detect body heat to automatically switch on when someone approaches. They are common on driveways, porches, and garden paths. When a sensor light misbehaves, the fault is usually in the PIR sensor module rather than the light itself. PIR sensors can fail due to age, water ingress, spider webs across the sensor lens, or incorrect sensitivity settings. The sensor module is a separate electronic component that can usually be replaced independently.
Common causes
- PIR sensor module has failed due to age or moisture
- Sensitivity set too low to detect movement at the required distance
- Spider webs, dirt, or condensation covering the sensor lens
- Sensor pointed at a heat source (boiler flue, air vent) causing false triggers or confusion
- Daylight sensor keeping the light off because it thinks it is still daytime
Is it dangerous?
A faulty sensor light is not dangerous. However, if the light is an important security feature, getting it fixed promptly is worthwhile. If the light stays on permanently and uses halogen bulbs, prolonged operation can cause overheating in enclosed fittings.
Can I fix it myself?
Clean the PIR sensor lens with a dry cloth to remove dirt, cobwebs, and condensation. Check the sensitivity and time settings — most PIR lights have small adjustment dials (usually marked sensitivity, time, and lux). Try resetting the light by turning it off at the switch for 30 seconds, then back on. Ensure the sensor is not pointing at a heat source or moving object like a tree branch. If the light comes on manually (via a switch or override) but not via the sensor, the PIR module has likely failed.
When to call an electrician
Call an electrician if the light does not work at all (not even manually), if you have tried adjusting settings and cleaning without success, or if you want the PIR sensor or entire fitting replaced. If the light is mounted high up and you cannot safely reach it, an electrician with appropriate access equipment should do the work.
What will an electrician do?
Test the light fitting to confirm it works independently of the sensor
Test and adjust the PIR sensor settings (sensitivity, timer, lux level)
Replace the PIR sensor module if it has failed
Check the wiring and connections at the fitting for corrosion
Reposition or replace the fitting if the sensor angle is problematic
Typical cost
£60 – £150
Adjusting settings and cleaning is at the lower end. A full sensor or fitting replacement with a new unit is at the higher end.
